Currently, animal models serve as gold standards for testing of drug efficacy or the effects of toxicants on the body. However, studies have shown that rodent and non-rodent animal species are predictive for human toxicity only 43% and 63%, respectively. Additional drawbacks associated with such models are high costs and low throughput. Given the drawbacks to animal use, efforts are ongoing to transition to in vitro tests. One serious drawback to in vitro tests is that they are restricted to a single cell/tissue type (liver, heart, lung, etc.) per well of microtiter plate; this prevents the evaluation of multi-organ effects. To overcome this limitation, chips containing cells or tissue have been linked through microfluidics. These systems have the key feature of utilizing pumps to drive the flow of tissue culture media over tissue cells unilaterally, thus simulating blood flow from one organ to the next as occurs in vivo. However, these systems are prone to contamination and are not compatible with standard laboratory analysis equipment such as microplate readers or microscopes. A need exists for improved model systems to assess drug efficacy and toxicant effects on the body.